Process of epitaxial growth wherein the distance between the carrier and the transfer material is adjusted to effect either material removal from the carrier surface or deposition thereon



3,425,878 TWE EN THE H. DERSIN ET AL WTH WHEREIN THE DISTANCE BE USTED ER MATERIAL REMOVAL FROM THE EON R A E s H I T L N A 06 I 6 R T9 E 1 T A O 6 M m m D. F Rb S O N F A E R M T H E R HI T D R NM AE R M F E A M o R AT C Feb. 4, 1969 PROCESS OF EPITAXIAL GRO United States Patent 3,425,878 PROCESS OF EPITAXIAL GROWTH WHEREIN THE DISTANCE BETWEEN THE CARRIER AND THE TRANSFER MATERIAL IS ADJUSTED TO EF- FECT EITHER MATERIAL REMOVAL FROM THE CARRIER SURFA'CE 0R DEPOSITIDN THEREON Hansjiirgen Dersin, Ottobrunn, near Munich, and Erwin Friichte, Munich, Germany, assignors to Siemens Aktiengesellschaft, Munich, Germany Filed Feb. 16, 1966, Ser. No. 527,983 Claims priority, application Germany, Feb. 18, 1965,

US. Cl. 148-174 11 Claims Int. Cl. H011 7/ 36 Our present application relates to a method of producing semiconductor devices through a monocrystalline growth of semiconductor layers by precipitation from a gaseous compound of the semiconductor material, upon a carrier, preferably monocrystalline, of semiconductor material. A method has already been proposed whereby through intensive local heating, the carrier is given, at the beginning of the growth process, a temperature which is equal or higher than that of the starting material. The starting material is transferred into a gaseous phase and is in direct heat contact with a heating table. The temperature is at a value such that the oxide layer present at the surface of the carrier is removed by a chemical reaction. This reaction keeps the temperature of the carrier lower during the actual growth process than that of the semiconductor material which is in direct heat contact with the heating table and is to be transferred into a gaseous phase.

By this method it is possible to remove the oxide layer present at the surface of the semiconductor wafer to be coated. This surface layer or damage layer, naturally has an adverse effect upon the growth process. Thanks to this method, the disadvantages are avoided which occur in previously known methods, and are caused by the fact that the temperature adjustment occurs from the heating table, through heat transfer.

The present invention constitutes an improvement of this proposed method. According to the present invention the carrier and the original material are spatially separated at the start of the growth process and heated simultaneously or sequentially. The distance between carrier and original material thereafter, is reduced to the optimum distance for carrying out the chemical reaction.

Preferably, one proceeds in the following manner: the original material is placed on a heating table whose height is adjustable. At the beginning of the growth process, the heating table is shifted out of the heating zone. Heating takes place by means of one or several induction coils which may be positioned stationary at the height of the carrier or their height may be adjustable.

Thus, two induction coils may be used, of which one is placed at the height of the carrier, the other at the height of the storage disc and they may either be heated at the same time or in sequence. For heating the induction coils either a common voltage source or two separate voltage sources is used. With the aid of these two induction coils, it becomes possible to heat original material and carrier simultaneously or in sequence, or to subject the same to a gas etching.

If a single induction coil is used, then it is preferably displaceably arranged and utilized in the respectively required positions. A spacer is used as a contact surface for the carrier, whose diameter is larger than the opening formed through projections provided in the reaction vessel. That is, the diameter of the central opening is somewhat smaller than the carrier diameter. The carrier may be coated with a disc of conducting material, especially carbon, to increase the heating etfect.

3,425,878 Patented Feb. 4, 1969 The reaction gas is a mixture of hydrogen and/or halogen, hydrogen halide, water vapor and a gaseous compound of a semiconductor material. The reaction gas is passed through the reaction vessel even during the preheating. If necessary, doping materials may be added to the reaction gas.

As soon as a sufiicient amount of the carrier has been removed, the heating table is shifted upward until the semiconductor material resting upon it comes into contact with the distance holder and thereby with the carrier on top thereof. In this position, the arrangement is held at a temperature of approximately 1250 C., until the desired layer thickness is obtained.

The method according to the invention is particularly suitable for the production of hetero junctions, since said method makes it possible to heat at different temperatures, the original material, which is to be transferred into a gaseous phase and the carrier is to be provided with a growth layer. In this manner, hetero junctions may be produced without difficulty, for example between the gallium arsenide and germanium or gallium arsenide and gallium phosphide.

Semiconductor devices produced, according to this method, are suitable for the production of semiconductor structural components, such as transistors, rectifiers, etc.

The invention will be described in greater detail in conjunction with the specific example relating to FIGS. 1 and 2.

A spacer holder 3 is placed upon projections 10 of a tubular reaction vessel of quartz or laboratory glass, which is equipped inside with two projections 10. A monocrystalline disc 4 of semiconductor material, whose diameter is somewhat larger than the opening 5 in the center of the spacer, is placed upon the latter. The monocrystalline disc 4 consists, for example, of n-conducting silicon, and serves as a substrate for the layer which is to be applied by the transport process. To increase the heating effect, a carbon disc 6 is provided and placed upon the carrier 4. Another disc 7 of semiconducting material serves as the initial (or starting) material and is placed on a heating table 8, of carbon or silicon carbide, SiC. The heating table 8 is moved up in the direction of an arrow 2, by means of a quartz rod 9. An induction coil 11 is provided for heating purposes, said coil being arranged, e. g. at the height of the carrier 4 displaceable in the direction of the arrow 12, as indicated in FIG. 2.

The device illustrated in FIG. 1, shows the geometric relation of initial material 7 and carrier 4 during the first phase of the reaction process. The heating effect is concentrated solely on the carrier 4, so that the latter has a considerably higher temperature, which results in the removal of the carrier surface by the reaction gas mixture flowing through the reaction vessel. The reaction gas is a mixture of hydrogen and/ or halogen, hydrogen halide, water vapor and a gaseous compound of the semiconductor material, for example SiHCl All materials which are inert at reaction temperatures are suitable materials for the spacer. Hence, SiO A1 0 SiC or carbon may be used. Favorably, the spacer is produced by using a 50500,U.I11 thick disc of inert material, through which an opening having a diameter less than the diameter of the carrie is bored.

If it appears desirable, prior to the growth process, to preheat also the disc comprising the original material, or to subject it to gas etching, it then is preferred that induction coil 11 be adjustable. In this case, the induction coil is displaceable upward or downward, in the direction of the arrow 12. One can proceed, for example in such a way that first the disc 7 constituting original material is heated and subsequently the induction coil 11 is so far shifted downward in the direction of the arrow 12, that the carrier 4 is heated to a temperature, necessary for the removing process.

If, in place of a movable induction coil 11, two different inducition coils are used, then it is preferred to arrange one coil at the same height as the carrier 4, and the other at the height of the heating table 8. The coils are then heated separately, so that following preheating, or after the gas etching, one of the induction coils, namely the one at the height of the heating table 8, is disconnected.

As soon as sufficient removal of the carrier surface is obtained, the heating table 8 is moved upwardly, by means of the quartz rod 9, and shown in FIG. 2, that the original material 7 contacts the spacer 3. The arrangement then corresponds to the sandwich arrangement customary in the execution of transport reactions. The heating effect is then primarily concentrated on the disc 7 comprising the original material. The carrier 4 resting on top, is heated by direct heat transfer and has now a temperature which is approximately 50 C. lower. In this condition, material is removed from disc 7 and precipitated on the carrier 4. The transport process is continued until the desired layer thickness has been obtained.

If the heating effect is to be even more localized upon the carrier or if necessary upon disc 7, then an induction coil may be used, whose height is adjustable. In the course of the reaction process, this coil is so displaced until the desired temperature curve is achieved.

If doped semiconductor layers are to be produced, then either disc 7, consisting of the original material may be provided with doping substances or the amount of dopant necessary to obtain the desired conductance or conductivity type, may be added to the reaction gas.

The method may also be utilized in the production of epitactic growth layers of various materials. Thus, it is possible to precipitate a germanium layer upon a monocrystalline carrier of gallium arsenide, or to precipitate a layer of gallium phosphide upon a carrier of gallium arsenide.

We claim:

1. In the method of producing a semiconductor device by monocrystalline growth of semiconducting layers onto a carrier of semiconducting material, the carrier is heated at the beginning of the growth process through a strong local heating effect to a temperature so high that the oxide layer at the surface of the carrier is removed through a chemical reaction occurring at this temperature, this temperature is at least as high as the temperature of a body of transfer material which is to be transferred into a gaseous phase and is in direct contact with a heating substrate, the temperature of the carrier during the actual growth process is maintained lower than the temperature of the material which is to be transferred into a gaseous phase, the improvement which comprises spatially separating at the start of the growth process, the carrier and the body of transfer material, heating said carrier to a temperature so high as to remove the oxide layer at the surface, heating said body of transfer material, reducing the distance between said carrier and said body to the distance necessar for carrying out a tansport reaction, reducing the temperature of the carrier body to the transport temperatue and thereafter carrying out the actual transport reaction.

2. The method of claim 1, wherein the transfer material is situated on a heating table, whose height can be adjusted and moving the heating table to a location outside of the heating Zone at the beginning of the growth process.

3. The method of claim 2, wherein at least one induction coil is used for heating purposes.

4. The method of claim 3, wherein an induction coil is used whose height is adjustable.

5. The method of claim 3, wherein two stationary induction coils are used.

6. The method of claim 3, wherein the carrier is placed upon a spacer, whose diameter is larger than the opening formed by projections provided in the reaction vessel, said spacer having a centered opening somewhat smaller than the diameter of the carrier.

7. The method of claim 6, wherein the carrier is coated with a layer of conducting material, particularly carbon.

8. The method of claim 7, wherein a mixture of hydrogen and a gaseous compound of the semiconductor material is passed through the reaction vessel during the preheating process.

9. The method of claim 7, wherein the heating table with the semiconductor material resting on it is moved after the preheating, upwardly so that the original material is brought into direct contact with the spacer.

10. The method of claim 9, wherein the transfer material placed into direct heat contact with the carrier, is kept at a temperature of about 1250 C. until the desired layer thickness is reached.

11. The method of claim 10, wherein doping substances are added to the reaction gas.

References Cited UNITED STATES PATENTS 3,142,596 7/1964 Theuerer 148175 3,172,792 3/1965 Handelrnan 148-175 3,208,888 9/1965 Ziegler et al. 148175 3,240,623 3/1966 Heim 117106 3,243,323 3/1966 Corrigan et a1. 156-17 XR 3,291,657 12/1966 Sirtl 148l75 3,316,130 4/1967 Dash et al 148-175 3,341,374 9/1967 Sirtl 148--175 3,359,143 12/1967 Hewang 148174 HYLAND BIZOT, Primary Examiner. PAUL WEINSTEIN, Assistant Examiner.

U.S. Cl. X.R. 

1. IN THE METHOD OF PRODUCING A SEMICONDUCTER DEVICE BY MONOCRYSTALLINE GROWTH OF SEMICONDUCTING LAYERS ONTO A CARRIER OF SEMICONDUCTING MATERIAL, THE CARRIER IS HEATED AT THE BEGINNING OF THE GROWTH PROCESS THROUGH A STRONG LOCAL HEATING EFFECT TO A TEMPERATURE SO HIGH THAT THE OXIDE LAYER AT THE SURFACE OF THE CARRIER IS REMOVED THROUGH A CHEMICAL REACTION OCCURRING AT THIS TEMPERATURE, THIS TEMPERATURE IS AT LEAST AS HIGH AS THE TEMPERATURE OF A BODY OF TRANSFER MATERIAL WHICH IS TO BE TRANSFERRED INTO A GASEOUS PHASE AND IS IN DIRECT CONTACT WITH A HEATING SUBSTRATE, THE TEMPERATURE OF THE CARRIER DURING THE ACTUAL GROWTH PROCESS IS MAINTAINED LOWER THAN THE TEMPERATURE OF THE MATERIAL WHICH IS TO BE TRANSFERRED INTO A GASEOUS PHASE, THE IMPROVEMENT WHICH COMPRISES SPATIALLY SEPARATING AT THE START OF THE GROWTH PROCESS, THE CARRIER AND THE BODY OF TRANSFER MATERIAL, HEATING SAID CARRIER TO A TEMPERATURE SO HIGH AS TO REMOVE THE OXIDE LAYER AT THE SURFACE, HEATING SAID BODY OF TRANSFER MATERIAL, REDUCING THE DISTANCE BETWEEN SAID CARRIER AND SAID BODY TO THE DISTANCE NECESSARY FOR CARRYING OUT A TRANSPORT REACTION, REDUCING THE TEMPERATURE OF THE CARRIER BODY TO THE TRANSPORT TEMPERATURE AND THEREAFTER CARRYING OUT THE ACTUAL TRANSPORT REACTION. 